107 Foot Drop and Peroneal Nerve Injury

Case 107 Foot Drop and Peroneal Nerve Injury

Robert L. Tiel

Clinical Presentation

An 18-year-old college freshman suffers a right knee dislocation during fall football practice.
He has immediate loss of dorsiflexion of the right foot on the field.
He is discovered to have an anterior and posterior cruciate ligament (ACL; PCL) and lateral collateral ligament tears.
He is scheduled for orthopedic knee surgery and his ligaments are repaired.
The peroneal nerve, which was seen in surgery, was believed to be “intact” but slightly bruised.
He is seen 4 months later in consultation with the following physical examination of his right leg.
Motor examination right lower extremity (Medical Research Council scale)
- Iliopsoas: 5/5
- Quadriceps femoris: 5/5
- Tibialis anterior: 0/5
- Extensor hallicis longus: 0/5
- Extensor digitorum communis: 0/5
- Peroneus longus/brevis: 3/5
- Posterior tibialis: 4+/5
- Plantar flexion (soleus/gastrocnemius): 4+/5
- Toe flexion: 4+/5
Sensory examination of the right lower extremity
- Web space between first and second toes numb to pin
- Dorsum of foot numb to pin
- Lateral border of foot slightly decreased compared with left foot
- Sole of foot same compared with the left foot
Deep tendon reflexes (DTRs)
- Right 2+ knee jerk (KJ) 1+ ankle jerk (AJ) (with reinforcement)
- Left 2+ KJ 2+ AJ

Questions

What physical finding must be checked on the football field and in the emergency room?
Is the nerve injured?
What is the Seddon or Sunderland grade?
Where is the nerve(s) injured?
Does the patient need any orthosis? If so what type?
Which plan of care should be arranged?
Which electrodiagnostic tests should be ordered and when? Which muscles should be examined?
When, if ever, should this nerve injury be explored?
What incision should be used? How do you find the peroneal nerve when all you see is fat? What is the relation of the common peroneal nerve to the fibular head?
When, if ever, should the nerve(s) be repaired?
What are the results of operative repair at this level for foot drop?
What are patient’s alternatives to nerve repair?

Answers

What physical finding must be checked on the football field and in the emergency room?

The most important physical finding in this case was the presence of a palpable distal pulse.
Unrecognized ischemia can lead to loss of limb and even death.
Using the Doppler ultrasound and/or angiography to assess the vasculature can further insure that the leg is viable.

Is the nerve injured?

Yes, there is no function of the muscles of dorsiflexion and no mention of direct injury to the muscles; so therefore the nerve is injured and not working properly after injury.

What is the Seddon or Sunderland grade?

The injury is either axonotmetic or neurotmetic by the Seddon classification or Sunderland grade 2–4 (Table 107.1).

Determining either the Seddon or Sunderland grade acutely is impossible upon initial presentation.

Because after 4 months, there has been no recovery of function, then this is not a neurapraxic injury – not a (Seddon) or a Sunderland grade 1 injury.

The Sunderland grade cannot be 5 as the nerve was inspected and appears to be in continuity.
Where is the nerve injured?
- Localization of the nerve injury is at the level of the peroneal division from the sciatic nerve.
- There is mild injury of the tibial division and complete injury of the peroneal.
- The peroneal nerve is tethered at this bifurcation and some damaging energy has been transmitted to the tibial nerve.
- The normal cross-sectional diameter of the sciatic nerve just proximal to the split is 11–12 mm, the tibial nerve is usually 6 mm and the peroneal nerve 5 mm at its origin.
- After a stretch injury these measurements increase and the peroneal nerve might be 11–12 mm and the tibial nerve 7 mm demonstrating the internal fibrosis and injury which accompanied the dislocation (Fig. 107.1).
Does the patient need any orthosis? If so what type?
- Almost all patients will benefit from a well-fitting orthosis.
- The most common is the in the shoe ankle-foot orthosis (AFO), but there exist many variations on this model. The specific purpose of an AFO is to provide toe dorsiflexion during the swing phase, medial and/or lateral stability at the ankle while standing, and, if necessary, push-off stimulation during the late stance phase.
- The goal of bracing is to prevent toe and foot drop while walking, which would contribute to tripping.
- Additionally, the ankle also needs the lateral support to avoid spontaneous inversion and twisting of the ankle joint.
- For those so inclined, a stiff lace-up work boot or a cowboy boot can reasonably serve these dual purposes.
Which plan of care should be arranged?
- The essential question with all nerve injuries and this one in particular is whether the nerve will recover spontaneously or not.
- Waiting 3–4 months is recommended unless evidence exists that the nerve is divided.
- Fitting for an orthosis and treating symptomatically for pain are both interventions usually warranted.
Which electrodiagnostic tests should be ordered and when? Which muscles should be examined?
- An isolated peroneal injury will not show involvement of the posterior tibial muscle.
When, if ever, should this nerve injury be explored?
- The nerve should be explored 3–4 months after injury if no recovery is observed and none demonstrated on EMG.1
- If EMG shows some recovery, it is worth waiting 8 weeks and repeating the clinical and if necessary electrical examination.
- When EMG recovery is not enough to power useful regeneration then operative repair is required.
What incision should be used? How do you find the peroneal nerve when all you see is fat? What is the relation of the common peroneal nerve to the fibular head?
- A “lazy S” incision on the back of the leg provides adequate “extensile” exposure and avoids going perpendicular to the knee flexion crease (Fig. 107.2).
- The tibial and peroneal nerves split from the sciatic at the lower third of the thigh (Fig. 107.3).
- The peroneal nerve lies along the medial edge of the short head and medial edge of the tendon of the biceps femoris, which is easily diff erentiated from the surrounding fat (Fig. 107.4).
- The peroneal nerve can be palpated at the fibular head.
- This is a point of fixation where the common peroneal nerve dives under the peroneus longus muscle.²
When, if ever, should the nerve(s) be repaired?
- The nerve should be repaired when no clinical or electromyographic evidence of recovery exists.
- Nerve action potential (NAP) recording can be done over the aff ected segment (Fig. 107.1).
- If a regenerative response is noted, then spontaneous recovery to M3 or greater will occur 90% of the time.
- If no recording is elicited, the damaged segment will be resected back to healthy, bleeding, and pouting fascicles and the gap repaired with sural nerve grafts.
- If the damaged segment is greater than 10 cm, orthopedic procedures of recovery with graft repair are so poor that closure may be all that is indicated at this time. An orthopedic procedure such as tendon transfer may then be contemplated at a later time.
What are the results of operative repair at this level for foot drop?
- The results of operative repair for peroneal nerve injury are very much distance dependent.
- Pooled literature shows a 29–50% recovery to M3 or greater with graft repair and a 39–100% recovery with primary suture repair.³
- Graft length is a determinate with 70% recovery for grafts <5 cm, 35% for grafts 6–12 cm and 18% for grafts over 12 cm.⁴
- Most knee dislocations injure the nerve from its fibular fixation into the sciatic bifurcation thereby requiring long grafts, usually greater than 12 cm, thus predicting poor results.
What are patient’s alternatives to nerve repair?
- Currently, no acceptable nerve transfers for this nerve injury exist.
- After a year without neurologic recovery, orthopedic solutions become necessary.
- The posterior tibialis tendon provides the energy of dorsiflexion.
- Depending upon the completeness of injury, different variations of tendon transfer are employed.⁵
- After minor recovery in the evertor muscles (M2), tibialis posterior transfer appears to be more eff ective.